Adaptive Predistortions Based on Neural Networks Associated with Levenberg-Marquardt Algorithm for Satellite Down Links

Rafik Zayani,Ridha Bouallegue,Daniel Roviras

doi:10.1155/2008/132729

Abstract

This paper presents adaptive predistortion techniques based on a feed-forward neural network (NN) to linearize power amplifiers such as those used in satellite communications. Indeed, it presents the suitable NN structures which give the best performances for three satellite down links. The first link is a stationary memoryless travelling wave tube amplifier (TWTA), the second one is a nonstationary memoryless TWT amplifier while the third is an amplifier with memory modeled by a memoryless amplifier followed by a linear filter. Equally important, it puts forward the studies concerning the application of different NN training algorithms in order to determine the most prefermant for adaptive predistortions. This comparison examined through computer simulation for 64 carriers and 16-QAM OFDM system, with a Saleh's TWT amplifier, is based on some quality measure (mean square error), the required training time to reach a particular quality level, and computation complexity. The chosen adaptive predistortions (NN structures associated with an adaptive algorithm) have a low complexity, fast convergence, and best performance.

Highlights

Satellite communication systems are developed to provide connectivity between remote terrestrial networks, direct network access, and Internet services using fixed or mobile terminals [1]
This paper presents adaptive predistortion techniques based on a feed-forward neural network (NN) to linearize power amplifiers such as those used in satellite communications
We review the different algorithms used in this investigation: gradient descent backpropagation (GD), gradient descent backpropagation with the momentum (GDm), conjugate gradient BP (CGF), quasi-Newton (BFG), and Levenberg-Marquardt (LM)

Summary

Introduction

Satellite communication systems are developed to provide connectivity between remote terrestrial networks, direct network access, and Internet services using fixed or mobile terminals [1]. Future generations of these systems are required to support higher transmission data rates for providing multimedia services. Among the most important challenges of satellite communications are spectral and power efficiencies [2]. In order to increase bandwidth utilization, several researchers are working to make use of high-level linear modulation schemes such as M-QAM and its multicarrier variant OFDM which can support bit rates of log2(M) bits/s in 1 Hz of bandwidth [3] and resists multipath fading and impulse noise [4]. Even if OFDM presents high power to average power ratio (PAPR), its utilization on satellite down links is interesting because of its spectral efficiency. Digital video broadcasting (DVB) for terrestrial networks uses OFDM modulation

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